26 MAXWELL'S LAW 



51 



cannot be immediately transferred to the resultant deviation 

 from the centre. The points that are equally distant from 

 the centre do not lie on a straight line, but on a circle 

 described about the centre; and the circle which passes 

 through the most shot-marks is by no means one of the 

 innermost circles of the target, for the inner rings are too 

 small to contain many marks in fact, the circle passing 

 through the most shot-marks lies on a ring of medium size. 

 The same relations hold also for the values of the speeds 



FIG. 1 



and of the components of velocity which occur the most 

 frequently among the molecules of gas. 



A more exact representation of the unequal probability 

 of different values of the speed is given by the curve on 

 page 52, the course of which shows us the law regulating the 

 number of molecules which move with a given speed. In 

 the figure the function which determines the frequency of a 

 value is represented by a curve with the equation 



419 x z 

 7T *X 6 ' . 



This construction means that the magnitude of the ordinal e 

 y of the curve is equal to the probability of a speed whose 



E 2 



